octy vrs vibration/rattle

Has anyone experienced a loud vibrating/rattle which appears to be coming from the floor near the drivers seat belt inertia?When shutting the drivers door it vibrates and when driving on our crap road surfaces.I have removed all trim plus seat belt inertia.By hitting the inside of the door pillar with my hand it sounds like it's under the floor.Some one has suggested it might be some seams on the floor pan need a bit of welding.Please help as i don't want to have to remove the whole of my interior to sort this out.And no before someone suggests it turning the radio up is not the solution.

Thanks to anyone with a suggestion.